Electric switch of the fluid flow type



Dec. 7, 1937. w. WALKER ELECTRIC SWITCH OF THE FLUID FLOW TYPE FiledOct. 29, 1935;

INVENTOR UNITED STATES PATENT OFFICE 2,101,115 emc'rarcswrrcn or'ruuFLUID FLOW me Warren E. Walker, Short Hills, N. 1., asslgnor to GeneralElectric Vapor Lamp Company, Hoboken, N. 1., a corporation of New JerseyApplication October 29, 1935, Serial No. 47,299

6 Claims. 01. (200-152).

The present invention relates. to electric switches of the fluid flowtype, and particularly to switches employing mercury to close thecircuit therethrough. 5 A particular object of the invention is toprovide a fluid flow switch having an extremely low The inventionconsists in the new and novel structure hereinafter set forth andclaimed.

15 In general the current rupturing capacity of a fluid flow switchconsiderably exceeds the current which the same switch can continuouslycarry with an approved temperature rise, and the rating of the switch istherefore necessarily limgo ited to the smaller value imposed by thelatter of these considerations. This limiting temperature rise withinthe switch is, of course, a direct function of the internal resistanceof the switch, and hence any decrease in this resistance is im- 5mediately reflected .in an increased rating for the switch. Accordinglya great deal of effort has been expended in an attempt to reduce theinternal redstance ofthese switches.

Recently considerable attention has been directed toward the developmentof switches having a metal envelope, in which different portions of thisenvelope serveas the electrodes. This construction has'providedelectrodes having a very considerable area in contact with the mercury35 commonly used as the fluid in these switches, and has thus tended toproduce a switch having a low internal resistance. This general idea ofa metal envelope switch has, of course, been toyed with for many years,but it isonly since the recent 40 development of switches of this typehaving vitreous seals, such as disclosed in an application by John H.Payne, Jr., Ser. No. 759,927, filed December 28, 1 934,'whereby they arehermeticallysealed for the first tim'e, that a successful commercial 45structure has been attained. The production of these vitreous seals,however, requires the use of a fusing heat and this heat, whileessential to the production of a successful tends to pro.- duce an oxidefilm on the surface of any of the 50 metals which it is practicableto-use for these envelopes. The presence of this film is indicated bythe fact that the resistance of these switches. while very low, issometimes above that which would be obtained with a clean metal surface55 which would be we by the mercury. Furthermore I have found that manyof the metal alloys which are commonly used in combination with softglass, such as the various chrome-iron alloys which it is known can besealed to the soft glasses, are not wet by mercury even when perfectlyclean.

I have now discovered that the resistance of any of these switches ismaintained at a constant low value by providing 'the inside of the metalshells forming the switch with a surface consisting of platinum, which Ihave found to be unique in possessing two essential characteristics forthis contact surface. Thus first of all the platinum does-not oxidizeduring the heating"-opera:'---- tions which are necessary to fusetogether the various elements of the switch, so that a clean metalsurface is presented to the mercury. Even more important this cleanplatinum surface 'is readily wet by the mercury to produce anexceptionally good electrical contact therewith, but is not dissolvedaway to any appreciable extent by the mercury, due to its low solubilitytherein, sothat an extremely thin film can be depended upon throughoutthe long life of the switch. It is not essential, or even desirable,that the platinum cover the entire inner surface of the metal shells,since I have found that a very small area there:

' of located on each shell where it will make contact with the mercurywhen the circuit through the switch is closed is entirely adequate togive an extremely low resistance, and that by heat? ing these areassomewhat toward the open circuit position of the switch the angle oftilt required to open and close the circuit is diminished.

The desired platinum surface is produced in any of a variety of ways.Thus in the preferred case a small piece of sheet iron coated with athin film of platinum on the exposed side is welded' in place in themetal shells. Or a fine wire sheathed in platinum, of the order of 10mils in 40 diameter, is welded end on to the metal shell and clipped oi!as short as possible. In either of these cases, of course, pure platinumcan also be used, but the use of an iron base for the platinum coatingspermits the use of larger pieces at the same small cost, and thus notonly simplifies the handling problem, but also exposes a larger surfaceto the mercury for a given quantity of platinum than would otherwise beconvenient. Likewise the'platinum may be coated on other base metals'which will not contaminate the mercury, if desired, although iron hasbeen found to be especially valuable for this use. As an alternative tothis welding the coating of the platinum is produced by depositing themetal out of a sus- Eli pension or solution of a salt thereof by any ofthe well known methods, or it can be plated on the shell.

In any of the above cases a small contact surface of platinum is formedat a point which is below the mercury in the closed circuit position ofthe switch which is not only free of oxide, but which is slightly wettedby the mercury, although it does not dissolve therein to any appreciableextent. This wetting of the contact surface results in an unusuallyconstant and good electrical conduction from the platinum to themercury, and as a result the internal resistance of the switchesconstructed in this novel manner is exceptionally low.

For the purpose of illustrating my invention I have shown a preferredembodiment thereof in the accompanying drawing, in which i Fig. 1 is anelevational view of a mercury switch having a hermeticallysealed metalenvelope,

Fig. 2 is a sectional view of the switch of Fig. 1,

Fig. 3 is an internal view of one of the metal sides of the switch ofFig. 1 before assembly showing a. piece of platinum or platinum coatediron welded thereto,

Fig. 4 is an elevational view of the refractory dividing member shown inthe position in which it is placed in the metal part shown in Fig. 3.

Fig. 5 is an enlarged section of a part of the metal side shown in Fig.3 showing the preferred mode of attaching the platinum,

Fig. 6 is a similar view to Fig. 5 showing a modification of thestructure thereof using wire, and

Fig. 7 is a side view of the switch of Fig. 1 showing the relation ofthe various parts thereof within the switch by means of dotted lines.

As shown in this drawing my novel switch, which is of the type disclosedin my co-pending application, Serial No. 28,560,1iled June 26, 1935, hastwo dished metal members i and 2 which areidentical, save that themember i has a filling opening therein. Between said members i and 2there is positioned a refractory dividing member 3' with a thin coatingof glass 4 hermetically sealing the members i and 2 to each other and tothe member 3. Within said switch there is a body of mercury 5 which isadapted to close the circuit between the members i and 2 through anopening 6 in the refractory 3 at' mercury 5 whenever said mercuryextends through the opening 6, and preferably at a point which is notquite opposite said opening, as best shown in Fig. 7, a piece of sheetmetal 8, which consists of platinum or platinum coated iron, is weldedto each of the 'metal members I and 2. In practice these metal stripsare of the order of 2 by 4 millimeters in size, and are oi 10 mil ironon which there has been rolled or otherwise placed a coating of platinumof the order of .2 mil in thickness.

In the alternative form of Fig. 6 a platinum or platinum sheathed wire Iof the order of 10 mils in diameter is welded end on to each of themetal shells, and the free end thereof then resistance and at the sametime economizeson the use of the platinum. In some cases the wire 8 iswelded on its side against the members I and 2, but in general betterresults are obtained with the structure shown for a given mass ofplatinum.

In the manufacture of these switches the platinum contacts 8 or 8 arewelded in place, as

shown, or an equivalent coating of the metal is deposited thereon fromsolution or suspension, by plating, or in any other suitable manner, andthe switch then assembled and fused together, preferably in the mannerdescribed in Payne's application or in my co-pending application,referred to hereinbefore. The contacts 8 or 8' remain unoxidized, ofcourse, despite the heating to which the members i and 2 are necessarilysubjected during the fusion step, due to the characteristics of theplatinum. After the switch has been evacuated it is given its filling ofmercury 5 and hydrogen and then sealed-off by fusing the closure l inplace.

The switch is then heated to a temperature of the order of C. while insuch a position that the mercury E is in contact with the contacts 8 ord, either by placing it in an oven or by passing a suitable currenttherethrough. This heating greatly facilitates the wetting of theplatinum by the mercury, with a resultant de crease in the contactresistance therebetween.

The contacts 8 or 8' are preferably positioned a little out of alignmentwith the opening 6, as shown, since in this position these contactsremain below the surface of the mercury as the switch is rotated betweenits open and closed clr cuit position. This prevents the attractionbetween the mercury and the wetted platinum from 1 exerting a drag onthe mercury on either movement of the switch, and thus results inoperation of the switch with a minimum angular movement thereof.

While I have described my invention by refer ence to a particularembodiment thereof it is to be understood that various changes,omissions and substitutions within the scope of the ap pended claims,may be made therein without departing from the spirit of my invention.

I claim as my invention&-

1. An electric switch comprising, in combination, a pair of metallicmembers hermetically sealed together to form a substantially all metalenvelope, said members being insulated from each other, mercury withinsaid envelope in contact with said metallic members over an extensivearea, said envelope having a relatively high con tact resistance withsaid mercury despite said large contact area, a refractory memberdividing said envelope into two chambers, said refractory member havingan opening therein to permit mercury flow therethrough in the closedcircuit position of said switch to electrically connect said metallicmembers, and a coating of platinum of relatively small area inelectrical contact with each of said metallic members and with saidmercury when said switch is in said closed circuit position to reducethe electrical resistance between said members and said mercury.

2. An electric switch comprising, in combination, a pair of metallicmembers hermetically sealed together to form a. substantially all metalenvelope, said members being insulated from each other, mercury withinsaid envelope in con-' tact with said metallic members over an extensivearea, said envelope having a relatively high contact resistance withsaid mercury despite said duce the electrical resistance between saidmemlarge contact area, a refractory member dividing said envelope intotwo chambers, said refractory member having an opening therein to permitmercury flow therethrough in the closed circuit position of said switchto electrically connect said metallic members, and a coating of platinumof relatively small area in electrical contact with each of saidmetallic members and with said mercury when said switch is in saidclosed circult position, said platinum coatings being wetted by saidmercury to make good electrical contact therewith to reduce theelectrical resistance between said members and saidmercury,

3. An electric switch comprising,in combination, a pair of metallicmembers hermetically sealed together. to form a substantially all metalenvelope, said members being insulated from each other, mercury withinsaid envelope in contact with said metallic members over an extensivearea, said envelope having a relatively high contact resistance withsaid mercury despite said large contact area, a refractory memberdividing said envelope into two chambers, said refractory member havingan opening therein to permit mercury flowtherethrough in the closedcircuit position of said switch to electrically connect said metallicmembers, and a coating of platinum of relatively small area inelectrical contact with each. of said metallic members and-with saidmercury when said switch is in said closed circuit position, saidcoatings being so positioned in an offset relation with respect to theopening in said refractory member that they are completely below thesurface of said mercury in both the open and closed circuit positionofsaid switch to rebers and said mercury.

4. In combination, a body of mercury, a metallic member of oxidizablemetal in extensive contact therewith, said memberhaving a relativelyhigh contact resistance with said mercury despite said extensive contactarea, and a coating of a non-oxidizable metal on a relatively smallportion of said member as compared to the' portion thereof in directcontact with said mercury, said coating being in contact with saidmercury to re-' duce thev resistance of the electrical path from saidmember to said mercury.

-5. In combination, a body of mercury, a metallic member of oxidizablemetal in extensive contact therewith, said member having a relativelyhigh contact resistance with said mercury despite said extensive contactarea, and a coating of platinum on a relatively small portion of saidmember as compared to the portion thereof in direct contact with saidmercury, said coating being in contact with said mercury to reduce theresistance of the electrical path from said mem-, her to said mercury.

6. A sealed device consisting in part of vitreous material, mercurywithin said device, a metallic member of oxidizable metal sealed to saidvitreous material and in extensive contact with said mercury, andacoating of platinum aflixed to a relatively small portion of saidmember as compared with the portion thereof which is in direct contactwith said mercury, said coating being in contact with said mercury to.reduce the electrical resistance of the path from said memberto i saidmercury.

WARREN R. WALKER.

